session - In PHP, is there any harm in running session_start() multiple times?

Question

Presumably there's some tiny performance hit, but beyond that?

Answer 1

As of PHP 4.3.3, calling session_start() while the session has already been started will result in an E_NOTICE warning. The second call to session_start() will simply be ignored.You could check if the session has been started first or not with:

if (session_id() == "")
  session_start();